Added a couple of lines to the Debian 12 notes to address

switch2osm#271

Author: Andy Townsend

serving-tiles/manually-building-a-tile-server-debian-12.md

@@ -96,6 +96,10 @@ Here we're assuming that we're storing the stylesheet details in a directory bel
     cd ~/src
     git clone https://github.com/gravitystorm/openstreetmap-carto
     cd openstreetmap-carto
+    git pull --all
+    git switch --detach v5.9.0
+
+The "git switch" is needed because that's the latest release that you can see at OpenStreetMap, but OSM Carto is in the process of moving to a different database format.  See OSM CArto's [INSTALL.md](https://github.com/gravitystorm/openstreetmap-carto/blob/master/INSTALL.md) for the newer version.
 
 Next, we'll check that we have installed a suitable version of the "carto" compiler.